Industry trends have led to a continuing increase in the number of transistors formed on a given substrate. Over the last four decades the semiconductor fabrication industry has been driven by a continual demand for greater performance (e.g., increased processing speed, memory capacity, etc.), a shrinking form factor, extended battery life, and lower cost. In response to this demand, the industry has continually reduced a size of semiconductor device components, such that modern day integrated chips may comprise millions or billions of semiconductor devices arranged on a single semiconductor die. Accordingly, the metal pitch of a semiconductor device has decreased to accommodate smaller transistors. A conventional semiconductor device includes a substrate, a circuit above the substrate, and metal lines that interconnect components of the circuit and that comply with electromigration (EM) rules.
EM is a phenomenon in which ions/atoms of a metal line of a semiconductor device migrate from a first region to a second region of the metal line and involves formation of voids at the first region of the metal line, which may cause an open circuit in the semiconductor device, and accumulation of the ions/atoms at the second region of the metal line, which may cause a short circuit in the semiconductor device. EM rules are established limiting a current flowing through a metal line to limit EM to an acceptable level.